The invention relates to a ring roller mill for grinding mineral clinker materials or the like and comprising at least one grinding ring and at least one roller as well as air inlet and air outlet openings for the passage of air.
Such mills may for example be used in connection with the production of cement where cement, slags or the like receive final grinding.
Compared to other roller grinding apparatuses, a ring roller mill is characterized in that the recycling of material may be effected inside the mill as it is also seen in e.g. a tube mill. However, it is a disadvantage of a tube mill that it is significantly more space-consuming than a ring roller mill of identical capacity.
Ring roller mills with and without air passage are commonly known, and the separation of finely ground material may for instance be effected by conveying a portion of the ground material to a sieve where material having a certain defined maximum grain size is separated off whereas the remaining material is recycled. Thus, material is recycled which comprises so small grains that, in such mills, operation problems in the form of vibrations often occur during fine-grinding.
In case of ring roller mills of the type disclosed above which are known from i.a. DE patent No. 667,011 and from U.S. Pat. No. 1,693,247, the air is caused to pass through the milling chamber along one single route, usually axially in the mill, which means that operation takes place at high air flow rates with ensuing losses of pressure in the volume flow rate of air which is necessary for the conveyance of the ground material out of the mills. Consequently the establishment of such air flow requires much power. Moreover, the large flow velocity means that particles having substantially larger grain sizes than desired are discharged from the mill. Therefore, such particles Bust be separated off and reconveyed to the mill. The known mills are associated with the additional disadvantage that a unilateral passage of air effects an accumulation of material at the one side of the mill thereby causing lop-sided operation with ensuing increased loads on roller, grinding ring, bearings, etc. Said disadvantages associated with the known ring roller mill, viz. a large power consumption and the necessary comprehensive reconveyance of material from a separation process to the mill, mean that, despite the disadvantages associated therewith, it has been preferred to use the tube mill rather than ring roller mills.